To safely and easily install the device in a dwelling house and to enable the use of sterilizing water in any required place and at any required point of time by placing a check valve for preventing the backflow of raw water to an electrolytic cell from being caused and automatically operating power supply systems to at least an automatic valve, an electrolytic stock solution supply pump and the electrolytic cell, with pressure switch signals.

In this device, when at least one of valves 8 placed in their respective service locations is opened, water pressure inside a main pipeline 10 is rapidly decreased and the decrease in water pressure is detected with a pressure switch 3, to start the operation of an electrolytic stock solution supply pump 5, to concurrently supply electric power to an electrolytic cell 6 and thereafter to open an automatic valve 1. The prepared electrolytic product is mixed with raw water beginning to flow down through the main pipeline 10 to form sterilizing water and the formed sterilizing water is supplied to each of the service locations in which the respective valves 8 are opened. Also, when all the valves 8 in their respective locations are closed, the water pressure inside the main pipeline 10 between the automatic valve 1 and the valves 8 is rapidly increased, however, the backflow of the raw water having the increased water pressure to the side of the electrolytic cell 6 is prevented from occurring by placing a check valve 7 for this purpose and the increase in water pressure is detected with the pressure switch 3 to concurrently stop all the power supply source systems to at least the automatic valve 1, electrolytic stock solution supply pump 5 and electrolytic cell 6.